Automatic defibrillator module for integration with standard patient monitoring equipment

ABSTRACT

A defibrillator module is described which includes a cardiac sensor, a pulse generator and a controller that generates commands responsive to intrinsic cardiac signals for the operation of said pulse generator. The defibrillator module synergistic and arranged so that it can be coupled to a generic patient monitor so that the two can share certain functions. For example, operational parameters and other signals indicative of the operation of the defibrillator module can be shown to the clinician by the patient monitor. Data between the defibrillator module and the patient monitor is exchanged using either a standard or a customized protocol.

BACKGROUND OF THE INVENTION

A. Field of Invention

This invention pertains to an external defibrillator module arranged andconstructed to provide anti-tachyarrhythmia therapy to a patient. Inparticular, an automatic external defibrillator module is describedwhich has several operational modes including a fully automatic mode inwhich shocks are delivered without any manual intervention, an advisorymode, a manual mode, and a pacer mode. Moreover, the invention pertainsto a defibrillator module which is arranged and constructed forintegration with patient monitoring equipment for sharing certainfunctions and information using a standard or customized protocol.

B. Description of the Prior Art

Defibrillators are devices which apply electric therapy to cardiacpatients having an abnormally high heart rhythm or fibrillation. Twokinds of defibrillators are presently available: internal defibrillatorswhich are implanted subcutaneously in a patient together with leadsextending through the veins into the cardiac chambers, and externaldefibrillators which are attached (usually temporarily) to the patient.External defibrillators are used in most instances in case of anemergency, for example, when a patient has either suffered cardiacarrest or when a cardiac arrest is imminent. Typically, thereforeexternal defibrillators are manual devices which must be triggered by aphysician or other trained personnel. Internal or implantabledefibrillators (and cardioverters) are implanted as a permanent solutionfor patients having specific well-defined cardiac deficiencies whichcannot be treated successfully by other means. They generally operate inan automatic mode.

Commonly-owned U.S. Pat. No. 5,474,574 discloses an externaldefibrillator. Commonly-owned U.S. Pat. Nos. 4,576,170 and 5,474,574,incorporated herein by reference discloses external defibrillators.

Several patient monitoring systems are presently available in modularform which allow a clinician or other health professional to monitor anddisplay various physiological parameters of a patient. Typically theseunits include several subassembly modules which cooperate to acquiredata from the patient, to store the data electronically and to displayinformation about a patient's physiological status. The systems may alsobe adapted to generate audible and/or visual alarms when certaincriteria are met. Some systems may also be integrated into acommunications network covering, for example, a part or even a wholehospital and on which data is exchanged for various purposes. Monitoringsystems of this kind are available from GE Marquette Medical Systems ofMilwaukee, Wis.; Agilent Technologies of Andover, Mass.; SpacelabsMedical of Redmond, Wash., and many other companies. However, typicallythese systems are passive in that their main purpose is to monitor,collect information and generate alarms. These systems cannot providetherapy.

OBJECTIVES AND SUMMARY OF THE INVENTION

An objective of the present invention is to provide an automaticdefibrillator module which is capable of detecting a current cardiaccondition of a patient and of providing appropriate therapy to thepatient, when needed.

A further objective is to provide an automatic defibrillator modulewhich can be interfaced with a existing or future patient monitoringsystems in a manner which allows the system and the module to shareinformation and other common functions.

Yet another objective is to provide an external defibrillator modulewith several modes of operation, including an automatic mode in whichshocks are applied on demand in accordance with preprogrammed shockparameters and without any prompting from an attendant, an advisory modein which an attendant is alerted to a shockable rhythm however theapplication of shocks must be initiated by the attendant, a manual modein which the attendant determines how and when shocks should be appliedand the preprogrammed shock parameters are ignored, and a pacer mode forpacing certain cardiac events.

Other objectives and advantages of the invention will become apparentfrom the following description of the invention.

Briefly, a composite monitoring system constructed in accordance withthis invention comprises a patient monitor including a sensor arrangedto sense a physiological characteristic of a patient and a signalprocessor coupled to said sensor and adapted to process the signal fromsaid sensor and an output member; and a defibrillator module adapted tobe selectively coupled to said patient monitor, said defibrillatormodule including a pulse generator responsive to commands to generatetherapeutic pulses for the patient, and a data generator arranged togenerate indication signals indicative of an operation of saiddefibrillator module; wherein said patient monitor and saiddefibrillator module cooperating when coupled to transfer saidindication signal to said output member whereby said output membergenerates output signals corresponding to one of said patientcharacteristic and said indication signals. The patient monitor mayinclude a display that can be used to show signals or data associatedwith either the physiological characteristics being monitored orinformation pertaining to the operation of the defibrillator module. Thepatient monitor could also include audible and visual alarms, a printer,and a connection to a network through which data could be sent to aremote location. All these components could be shared between thepatient monitor and the defibrillator module. Data between thedefibrillator module and the patient monitor is exchanged using either aprotocol standardized for the monitor or by using a customized protocol.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows a block diagram of a combined patient monitor and automaticdefibrillator system;

FIG. 2 shows a somewhat schematic isometric view of the automaticdefibrillator module for the system of FIG. 1; and

FIG. 3 shows a block diagram for the control assembly of the automaticdefibrillator module incorporated into the system of FIG. 1;

FIG. 4 a shows a circuit illustrating the “totem-poling” of two SCRs sothat the combination of the two devices can withstand a higher voltagethan a single device;

FIGS. 4 b, 4 c and 4 d are, respectively, the substrate construction,circuit symbol and I=V characteristics of a Shockley diode;

FIG. 4 e is a circuit diagram of a breakover USD;

FIGS. 4 f, 4 g and 4 h are, respectively, a circuit diagram, circuitsymbol and I=V characteristics of a breakunder USD;

FIGS. 5 a and 5 b are, respectively, the circuit symbol and a circuitdiagram for a breakunder USD with hysteresis;

FIG. 6 is a circuit diagram of a defibrillator using a firstimplementation for the pulse generator;

FIG. 7 is a circuit diagram of a of defibrillator using a secondimplementation of a pulse generator;

FIG. 8 is an example of the waveform that can be produced by theimplementation of FIG. 7;

FIG. 9 is a circuit diagram of a defibrillator showing a thirdimplementation of the pulse generator;

FIG. 10 is a circuit diagram of a fourth implementation of the pulsegenerator;

FIG. 11 illustrates a pulse generator with the output circuit beingimplemented as a single encapsulated integrated circuit component;

FIG. 12 a is a circuit diagram of a fifth implementation of the pulsegenerator; and

FIG. 12 b is an example of the waveform that can be produced by theembodiment of FIG. 12 a.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1, a combined system 10 constructed in accordancewith this invention includes a generic patient monitor 12 which isconnected to one or more sensors 14 extending to the patient (notshown). The sensors 14 are used to obtain one or more physiologicalindicia from the patient, such as temperature, pressure, heart rate,respiration function, and so on. The monitor 12 includes a dataprocessor 16, a display 18, a power supply 20, and data interface 22,which may for example be a standard serial or parallel port or any otherdata interface that may be used to exchange information with othercomponents and/or a communications network (not shown). The monitor 12may also include an audible alarm 24, a visual alarm 26 and a printer28.

The data processor 16 in monitor 12 collects information from thepatient through the sensors, processes this information and based on itsprogramming, generates reports on the status of the patient. This statusmay be shown on display 18, and selectively a hard copy of the reportsmay be provided by printer 28. The status information may also betransmitted to remote locations via the interface 22 and thecommunications network. The monitor 12 may also include a memory 30 forlogging the information regarding the status of the patient. The dataprocessor 16 may also be adapted to determine if certain of thephysiological parameters exceed certain preselected ranges or thresholdvalues, these ranges or threshold values being selected to correspond toindicate abnormal or dangerous conditions for the patient. When such anevent is detected, the data processor can activate the audible and/orthe visual alarms 24, 26 to indicate that a danger condition has beendetected.

As seen in FIG. 1, associated with monitor 12 there is provided anautomatic defibrillator module (ADM) 32. The ADM is connected to its ownset of sensors or defibrillator pads 34 via a cable 36. The purpose ofproviding the ADM 32 as a module rather than a stand-alone unit is sothat it can share some of the functions and components of the monitor12. For this purpose, the ADM 32 is connected to monitor 12 via a datacable 38 which acts as an output member and interfaces the ADM 32 withthe monitor 12 as described in more detail below. Power to the ADM 32can be provided by the power supply via a cable 40, or alternatively,the cable 40 may be connected to a standard line voltage outlet (notshown).

Referring now to FIG. 2, the ADM 32, in this configuration, consists ofthree assemblies: a battery pack 42, an assembly 44 including an ACpower supply and biphasic pulse generator and a control board 46. Thebattery pack 42 consists of one or more batteries, which may bere-chargable by using energy from the AC power supply. The AC powersupply is connected by cable 40 to monitor 12 or other line voltagesource. The battery pack is used to provide high energy to the biphasicpulse generator of assembly 44. This energy is used as backup powersource in the event of a AC power failure. The defibrillation pulses aretransmitted by the cable 36 to the patient. For this purpose, theassembly 44 the cable 36 is provided with a connector 48 which mateswith a connector 50 on the assembly 44.

The control assembly 46 contains the components required to control theoperation of the ADM 32. As seen in FIG. 2, the assembly 46 includes afront face 52 formed with a display 54. Also provided on face 52 are acontrol knob 56 and a plurality of panel switches 58. Built into each ofthe switches 58 is an indication light 60. These lights are optional andmay be omitted.

The control assembly 46 is further provided with two serial ports 62,64. Serial port 62 is connected via cable 38 to monitor 12. The otherport 64 may be used to connect the ADM 32 to other components.

The overall functionality of each component is more important than thenumber and the functional partition of assemblies. Anotherimplementation may comprise more or less assemblies.

FIG. 3 shows a block diagram of the ADM 32. The control assembly 46includes a microprocessor or controller 66, a flash memory 68 and acustom control IC 70 which may be made using, for example, an FPGAdesign. The microprocessor 66 is connected to the serial port 62,switches 58, indicator lights 60 and the flash memory 68 and the customIC 70 so that it can control the operation of the ADM 32. The flashmemory 68 is used to store various operational parameters of the ADM 32which can be either preset or selected by a clinician. These parameterscan be set through the menu control knob 58 in conjunction with theswitches 60 or via the patient monitor.

The lights 60 are activated either by the microprocessor 66 or by thecustom IC 70. As discussed above, the ADM 32 is capable of generatingaudible as well as visual indication signals. The audible signals can betransmitted to the monitor 12 and/or to external speakers 72 (not shownin FIGS. 1 and 2). These audible signals can be generated by themicroprocessor 66 and/or the custom IC 70.

Component 50 includes a power supply 74, a battery charger 76, an alarmpower unit 78 and a biphasic pulse generator 80 (all shown in FIG. 3).The alarm power unit 78 provides the power required to drive thespeakers 72 (if present). The battery charger 76 is used to charge thebattery pack 42.

The biphasic pulse generator 80 receives dc power either from the powersupply 74 or from the battery pack 42. The pulse generator 80 generatesbiphasic pulses in accordance with commands from the microprocessor 66.

A somewhat preferred implementation for the biphasic pulse generator 80is now described, it being understood that this implementation does notconstitute a part of the subject invention, and that otherimplementations may be used as well.

The pulse generators described herein use devices or circuits having thecharacteristics of Shockley diodes, and which are referred to herein asuncontrolled solid state devices (USDs) as defined above. Unlike SCRsand IGBTs, a Shockley Diode does not require a gate drive signal toinitiate it from a high impedance state to a state of lower impedance.FIG. 4 b shows the substrate construction of a Shockley diode as a fourlayer silicon device with respective doping densities P1, N1, P2 and N2.

FIG. 4 c shows the symbol used to denote a Shockley diode; note thatthere are only two connecting terminals. Essentially, a Shockley diodeis unidirectional in that it can only change from its default highimpedance state to a state of reduced impedance when the polarity of theapplied signal is in a particular direction to forward bias the device,see FIG. 4 d. Applying a signal of opposite polarity will fail to changethe device's state unless the voltage exceeds its reverse breakdownvoltage (Vr). A characteristic of a Shockley diode is that as a voltageis applied across the device in the forward bias direction, the devicewill only change to its lower impedance state if the voltage exceeds apredetermined threshold (Vth). Shockley diodes, however, are not readilycommercially available and those that are typically only capable ofwithstanding small voltages and currents. However, this limitation canbe overcome by arranging other commercially available devices to performthe equivalent function for high voltages and currents.

FIG. 4 e is a high voltage, high current, implementation of a“breakover” USD, equivalent to a Shockley diode, using a DIAC and aTRIAC. Note that the overall circuit of FIG. 4 e has only two terminals,an anode A′ and a cathode K′. The TRIAC will change to a state of lowimpedance allowing a high current to flow when an appropriate voltage isapplied to its gate terminal g. The combination of resistors R1 and R2form a voltage divider, dividing the voltage V down to a voltage Vb,referenced to the cathode K′, at the base of the transistor T1, whereVb=V[R2/(R1+R2)]. The emitter follower configuration of transistor T1keeps the voltage applied to the DIAC at point X at approximately 0.7Volts below the voltage Vb.

The DIAC will remain in its default high impedance state unless thevoltage across it exceeds its threshold voltage Vd. Unless this voltagethreshold is exceeded therefore, the USD will remain high impedancebetween A′ and K′. If, however, the voltage at X exceeds the DIAC'sthreshold Vd, the DIAC will fold back and allow a voltage to appear atthe gate of the TRIAC, and the TRIAC will then change to its lowimpedance state allowing a high current to flow between A′ and K′. Theoverall voltage at which the USD changes state can therefore beaccurately set by the voltage divider R1/R2. If the USD is desired tochange to its low impedance state when the voltage V across it, i.e.across the terminals A′ and K′, reaches a certain threshold Vth, thenthe values of R1 and R2 are chosen such that this voltage Vth causes thevoltage at X to be equal to the DIAC threshold voltage Vd; i.e. onesolves the equation Vd=[Vth(R2/(R1+R2))]−0.7 for R1 and R2. Resistor R3limits the current flow into the gate terminal of the TRIAC and preventsthe gate from being damaged by the relatively high voltage across theterminals A′ and K′. Note that with the state change of the device beingdetermined by the ratio of R1 and R2, and the supply to the DIAC beingperformed by R3 through the current gain of T1, the values of both R1and R2 can be kept high. Using high impedance values for R1 and R2 meansthat in the high impedance state there is very little current leakagethrough the USD. The diode D1 opposes any current flow in the reversebias direction and in effect determines the reverse breakdowncharacteristics for the USD.

Note that any device which can be placed in a low impedance state froman initial state of high impedance could be used in place of the TRIACin FIG. 4 e, for example the USD could have employed a combination ofIGBTs, SCRs, FETs (field effect transistors) or BJTs (bipolar junctiontransistor). The various implementations possible will be known to thoseskilled in the art.

FIG. 4 f shows another USD where the device has been configured tochange to a state of low impedance if the instantaneous voltage acrossthe anode A′ and cathode K′ exceeds a well defined threshold Vl, yetdoes not exceed an even higher voltage threshold Vh. In other words, ifthe voltage V applied across the device in FIG. 4 f is within a wellspecified range from Vl to Vh the device will enter its low impedancestate, while if it is outside this range, the device will remain in itsdefault high impedance mode. With this particular characteristic thedevice is termed a “breakunder” USD. FIGS. 4 g and 4 h show the device'scircuit symbol and I−V characteristics respectively.

The implementation of the breakunder USD in FIG. 4 f is similar to thatof the breakover device in FIG. 4 e. The main difference is the presenceof a capacitor C1 and a second transistor T2. Capacitor C1 limits therate of change of voltage across R1. This in turn limits the rate ofchange of voltage across the DIAC. Since the voltage across the DIAC isslow to rise, if the voltage Y at the base of T2, as determined by thevoltage divider R4/R5, rises above the forward bias voltage across T2'sbase emitter-junction before the DIAC voltage reaches its threshold Vd,the transistor T2 will turn on to short the gate of the TRIAC to K′ andthus inhibit any current flow into the gate of the TRIAC. Using thisarrangement, the upper voltage threshold Vh can be set by the voltagedivider R4/R5 and the lower threshold Vl can be set as before by R1/R2.

Any breakunder device can further be arranged so that, once a voltagehas been applied across its terminals large enough to exceed the upperthreshold Vh so keeping the device in the high impedance state, if theapplied voltage drops in magnitude the device will remain in the highimpedance state. In this mode, in order to change to the low impedancestate, the current must be reduced to almost zero and then re-applied.This later device is referred to as a breakunder USD with hysteresis.

FIG. 5 a shows the circuit symbol for a breakunder USD with hysteresis.FIG. 5 b shows an implementation of the device based upon the breakunderdevice shown in FIGS. 4 f–h. Only the differences will be described. Atransistor T2 now forms a second emitter follower supplying a secondDIAC, DIAC2. The voltage at point Y is designed to have a value equal tothe threshold of DIAC2 when the voltage V across A′, K′ is equal to anupper threshold Vh. From FIG. 5 b it can be seen that, unlike thevoltage at point X, the voltage at point Y will instantaneously follow Vand will be a proportion of V according to the ratio set by R4 and R5.If the voltage V causes the voltage at Y to exceed the voltage thresholdof DIAC2, then a second TRIAC, TRIAC2, will enter a low impedance state.As soon as TRIAC2 enters its low impedance state, the voltage Vb at thebase of T1 will reduce to almost zero. Once TRIAC2 has entered a lowimpedance state T1 cannot supply any current to DIAC1 and therefore thegate of TRIAC1. This “feedback” enhancement of FIG. 4 has introduced alevel of hysteresis in to the arrangement. The only way now for TRIAC1to enter its low impedance state is for the voltage across A′, K′ to bereduced to zero and then a new voltage applied which has a value betweenthe lower threshold set by R1, R2 and DIAC1 and the upper threshold setby R4, R5 and DIAC2. This device has essentially three modes, two highimpedance and one low impedance. If the instantaneous voltage applied tothe arrangement is below the lower threshold Vl, then the combination ofR1, R2 and T1 means that DIAC1 does not pass current and TRIAC1 remainsin it's high impedance state. If the applied voltage is greater than thelower threshold Vl and less than the upper threshold Vh, then thecombination of R4, R5 and T2 means that DIAC2 does not pass current andwith DIAC1 now passing current, once the voltage across C1 has hadsufficient time to rise, to the gate of TRIAC1, TRIAC1 enters its lowimpedance state. If, however, the applied voltage is greater than theupper threshold Vh, then the combination of R4, R5 and T2 means thatDIAC2 does pass current to the gate of TRIAC2 thereby inhibiting DIAC1and keeping TRIAC1 in its high impedance state.

It should be noted that any of the USDs of FIGS. 4 e to 5 could beimplemented as doped silicon layers in a single discrete integrateddevice. None of the devices require any external control and have thecharacteristic that they will conduct if the voltage across their twoterminals A′ and K′ is either above and/or below a specified threshold.Another characteristic is that once in their low impedance state, theycan only be returned to their high impedance state if the current flowthrough them is reduced to near zero. At exactly which current they willdrop-out is dependent upon the particular device used.

FIG. 6 shows a basic implementation of a defibrillator, designed toprovide a monophasic output voltage pulse across a pair of patientelectrodes A and B. The defibrillator has an energy source 160, in thisinstance a capacitor which is charged up by a charging circuit 162, andan output circuit for connecting the voltage on the capacitor across theelectrodes A, B upon the occurrence of a control signal 164. The outputcircuit comprises a first current path connecting the +ve side of theenergy source 160 to the electrode A and a second current pathconnecting the −ve side of the energy source to the electrode B. Thefirst current path contains a breakover USD, USD1(bo), while the secondcurrent path contains an IGBT, IGBT1. The breakover USD1(bo) will allowthe current from the energy source 160 to flow through the load(patient) connected across the output electrodes A and B if the voltageapplied from the energy source is large enough to exceed its threshold.The breakover USD1(bo) can be constructed as described with reference toFIG. 4 e.

Initially, both sides of the load see a high impedance into A and B.Applying a gate drive pulse 164 to IGBT1 turns the latter on and dropsthe entire energy source voltage across USD1(bo). Provided the energysource is charged to a voltage above the threshold for USD1(bo), thelatter will change to its low impedance state. The energy source nowbegins to discharge into the load. Removing the drive pulse 164 from thegate of IGBT1 after a pre-determined time period causes IGBT1 to returnto its high impedance state and the current in the circuit reduces toapproximately zero. With almost zero current flow, the device USD1(bo)recovers and the load once again sees a high impedance on both sides ofA and B.

The use of the USD between electrode A and the +ve terminal of theenergy source means that there is no isolated controlling circuitconnection required. The only controlling element in the circuit of FIG.6 is the gate of IGBT1 and this is referenced to the circuit ground sono isolation barrier is needed. The conventional diode D1 is used toprevent current flow back into the charging circuitry when charging iscomplete. The output generated by the circuit of FIG. 6 is a simplemonophasic truncated exponential waveform.

Although FIG. 6 shows only one USD in the first current path, it will beunderstood that the voltage that can be withstood by the output circuitin the high impedance state can be increased by totem-poling two or moreUSDs in the first current path, as described previously. Two or moreUSDs in series actually behave just like a single USD with a thresholdVth which is the sum of the thresholds of the individual devices.

FIG. 7 shows an implementation of a defibrillator designed to provide abiphasic truncated exponential output voltage pulse across the patientelectrodes A and B. Essentially, the implementation of FIG. 6 has beenmodified to add third and fourth current paths, shown by dashed lines.The third current path connects the +ve side of the energy source 160 tothe electrode B and the fourth current path connects the −ve side of theenergy source to the electrode A. The third current path contains two“totem-poled” SCRs, SCR1 and SCR2, while the fourth current pathcontains a further IGBT, IGBT2. The first and second current paths areas before, except that the first current path is shown with twototem-poled breakover USDs, USD1(bo) and USD2(bo). The USDs may be asshown in FIG. 3. For reasons previously described, the SCRs haveisolated gate drives.

In operation, the energy source 160 is first charged to a voltageexceeding the threshold Vth of the totem-poled USDs. Then, at time t0(see FIG. 8), the device IGBT1 is given a gate pulse 64 placing it intoits low impedance state. This places substantially the entire voltage ofthe energy source across the totem-poled USDs (two USDs are used aspreviously stated to increase the voltage that the circuit canwithstand). The USDs therefore turn on (the devices SCR1, SCR2 and IGBT2remaining in their high impedance state), and a current flows throughthe load from electrode A to electrode B. As energy is removed from theenergy source by the load, the voltage applied by the energy sourcedecays. At a later time t1, the IGBT1 has its gate signal removed and itreturns to its high impedance state. This causes the current in thecircuit to reduce to almost zero so returning the devices USD1(bo) andUSD2(bo) to their high impedance states. The instant t1 is chosen sothat at that point the voltage remaining on the energy source is belowthe threshold Vth of the totem-poled devices USD1(bo) and USD2(bo).

Now, at a time t2 following shortly after t1, the devices IGBT2, SCR1and SCR2 are given simultaneous gate drive pulses 64′ to place them intheir low impedance state. Now a discharge current flows in the oppositedirection through the load, i.e. from electrode B to electrode A. Aftera further pre-determined time period has elapsed the gate drive todevice IGBT2 is removed at t3 and the current flowing in the circuit isreduced almost to zero. Again this causes the two SCRs to also return totheir high impedance state. The resulting output is as shown in FIG. 8.

In this circuit isolated gate drives are required for the SCRs. However,only two such isolated gate drives are required in this case. Themethods used by prior art would have required at least four isolatedgate drive circuits. Also only four devices are required to becontrolled in total instead of the six control lines previouslynecessary.

FIG. 9 shows a third implementation of the pulse generator. This differsfrom the implementation of FIG. 7 in that the totem-poled SCRs, SCR1 andSCR2, have been replaced by totem-poled breakunder USDs with hysteresis,USD3(bu) and USD4(bu).

In operation, the energy source 160 is first charged to a voltagegreater than the threshold Vth of the totem-poled breakover USDs andalso greater than the upper voltage threshold Vh of the totem-poledbreakunder USDs. Then, at time t0 (see FIG. 8, which also apples in thiscase), the device IGBT1 is given a gate pulse 164 placing it into itslow impedance state. This places substantially the entire voltage of theenergy source across the totem-poled breakover USDs, USD1(bo) andUSD2(bo). All other devices remain in their high impedance state (thebreakunder USDs because the voltage is above their upper threshold Vh;this is important because otherwise they would turn on and bypass theload). The breakover USDs therefore turn on and a current flows throughthe load from electrode A to electrode B. As energy is removed from theenergy source by the load, the voltage applied by the energy sourcedecays. At a later time t1, the IGBT1 has its gate signal removed and itreturns to its high impedance state. This causes the current in thecircuit to reduce to almost zero so returning the devices USD1(bo) andUSD2(bo) to their high impedance states. The instant t1 is chosen sothat at that point the voltage remaining on the energy source is belowthe threshold Vth of the totem-poled devices USD1(bo) and USD2(bo) butbetween the upper and lower voltage thresholds Vl, Vh of the totem-poleddevices USD3(bu) and USD4(bu).

Now, at a time t2 following shortly after t1, the device IGBT2 is givena gate drive pulse 64′ to place it in its low impedance state. Now thedevices USD3(bu) and USD4(bu) turn on, because the voltage appliedacross them is between their upper and lower voltage thresholds, and adischarge current flows in the opposite direction through the load, i.e.from electrode B to electrode A. After a further pre-determined timeperiod has elapsed the gate drive to device IGBT2 is removed at t3 andthe current flowing in the circuit is reduced almost to zero. Again thiscauses USD3(bu) and USD4(bu) to return to their high impedance state.The resulting output is as shown in FIG. 8.

Of particular note is that for this arrangement there are no isolatedconnection gate control connections to any of the devices in thecircuit. Also only two devices (IGBT1 and IGBT2) require control signalsand these are both direct electrical connections referenced to circuitground. This is a significant saving in size and component cost.Furthermore, to control the entire circuit only requires two controlsignals rather than the five that would be otherwise be necessary. Thecontrol circuit can now simply pulse one IGBT, IGBT1, to produce thefirst phase of the output waveform and pulse the second IGBT, IGBT2, toproduce the second phase of the output.

FIG. 10 shows a fourth implementation of the pulse generator. Thisdiffers from the implementation of FIG. 9 in that the two IGBTs, IGBT1and IGBT2, have been replaced by a breakover USD, USD5(bo), and abreakunder USD, USD6(bu), respectively. Also, an IGBT (IGBT3) has beenadded in common to the second and fourth current paths. For simplicitythe circuit uses single USDs (USD1(bo) and USD3(bu) respectively) in thefirst and third current paths, although as described two or more suchdevices can be totem-poled in each path to increase the ability of thecircuit to withstand higher voltages. Although this arrangement hasadded another circuit element, IGBT3, the output circuit is fullyautomatic and all devices connected to the load across A and B areuncontrolled. The only controlling signal required is the signal to thegate of IGBT3 in the common ground return.

In operation, having charged the energy storage device 160 to a voltagegreater in magnitude than the threshold of breakover devices USD1(bo)and USD5(bo), and also high enough not to enter the threshold rangewhich would place USD3(bu) and USD6(bu) into their low impedance state,a gate drive pulse 64 applied to IGBT3 will turn on USD1(bo) andUSD5(bo) and cause current to follow through the load in the directionfrom A to B. Removing the gate drive to IGBT3 after a pre-determinedtime interval will, as before, reduce the current in the circuit toalmost zero and all devices will return to their high impedance states.Provided the voltage across the energy storage device is now less thanthe threshold for USD1(bo) and USD5(bo), and furthermore providing thevoltage is within the threshold required to allow the break-underdevices USD3(bu) and USD6(bu) to enter their low impedance states, theapplication of a second gate pulse 164 to IGBT3 will cause the currentto flow through the load in the opposite direction from B to A. Again,this causes the biphasic waveform of FIG. 8 to be generated.

Note that not only is there no requirement for any isolated connectionsto any of the devices but only one single device needs to have a gatedrive signal applied in order for the whole circuit to be fullyoperated. It will be appreciated that this arrangement means that thewhole output circuit including USD1(bo), USD5(bo), USD3(bu), USD6(bu)and IGBT3 could be easily implemented as a single integrated solid statecomponent. This would further mean that the entire output stage would bea single encapsulated integrated module only requiring 5 connections.These connections would be a common ground connection, an input from anenergy source, two output connections to the electrodes A and B and asingle input control connection referenced to the common ground whichwould control the module. FIG. 11 shows the block diagram of a circuitincluding such an integrated circuit 66—note that even the gate drivecircuit for the IGBT can be included in the module, leaving the controlterminal into the circuit requiring a standard TTL type signal. Thisrepresents an enormous saving in terms of cost, size and complexity.

In a fifth implementation of the pulse generator, which is amodification of that shown in FIG. 10, and may likewise be formed withthe output circuit as a single integrated circuit component, the energysource is a programmable active power supply 168, rather than a passivecapacitor. Referring to FIG. 12 a, here the energy source is designed tosupply a programmed constant DC voltage, and with this voltage set at alevel above the conducting threshold Vth of breakover devices USD 1(bo)and USD5(bo) and greater than the low impedance threshold range ofbreak-under devices USD3(bu) and USD6(bu), the current again flowsthrough the load from A to B. Setting the programmable power supply thento supply a voltage of zero volts for a pre-determined time intervalcauses all the devices to return to their high impedance state. Furthersetting it to supply a voltage which is less than the thresholds forUSD1(bo) and USD5(bo), and within the threshold range required to allowthe breakunder devices USD3(bu) and USD6(bu) to enter their lowimpedance state, will cause the current to flow in the oppositedirection from B to A. The resulting waveform can be seen by way ofexample in FIG. 12 b. It would also be possible to have several energysources selectable by placing additional USDs within the circuitarrangement. Which energy source is to be used to supply the outputcircuit could then be selected at whatever times are desirable toachieve the pulse shape required.

It should be appreciated that further current paths containing USDs orother solid state devices could be added between the energy source andthe electrodes A and B in any of the circuits described above, therebyallowing a third, fourth or subsequent phase to be added in apre-determined polarity.

It should also be appreciated that further protective components may benecessary for reliable operation of the circuits in practice. By way ofexample, an inductor could be placed in series with the output of theenergy source to limit the rate of change of current in the circuit.Such additions are well known to those skilled in the art.

In FIGS. 1–3 the cable 36 terminating in connector 48 may have severalwires. In FIG. 3 three such wires are shown, 48A, 48B and 48C. Wires 48Aand 48B provide a dual purpose. They are used to sense intrinsic cardiacactivity, i.e., an ECG. Sensed signals are sent to the custom IC 70which performs signal processing on these signals and then sends them tothe microprocessor 66. The microprocessor uses the ECG to determine thecurrent condition of the patient.

The second function of the wires 48A, 48B is to provide defibrillatorpulses from the pulse generator 80.

An impedance detection circuit 82 may also be provided. This circuit maybe connected across the wires 48A, 48B and used to detect the impedanceof pads (not shown) used to apply the defibrillator pulses. Thisimpedance is provided to the custom IC 70 and may be used to confirmthat the wires 48A, 48B are not open and that the pads are attached tothe patient properly.

Preferably the cable 36 and its terminating block 34A which are uniquelyidentified by an ID code stored in a memory 84. The terminating block 34is connected to the electrodes or pads attached to the patient (notshown). The code stored in memory 84 can be obtained by the custom IC 70using the third wire 48C. This code is checked before any pulses areapplied to insure that the proper cable is used with the ADM 32.

The ADM 32 is operated as follows. First, it is attached mechanicallyand electrically to monitor 12 so that the two can form a single,integrated, composite system 10. The mechanical connection is notdescribed here since it can be implemented using brackets or othercoupling elements well known in the art. The electrical connectionsinclude the cable 40 for the power supply (if used) and a serial cable38.

Once the ADM 32 is mounted, it can be configured, for the patient. Forthis purpose, the clinician operates the keys on face 52 to enter into aconfiguration mode or via the patient monitor. In this mode theclinician can select the parameters associated with the defibrillatortherapy to be administered to the patient. The clinician can also setwhether the ADM 32 operates in a fully automatic mode, an advisory mode,a manual mode, or a pacer mode. Typically, in an automatic mode the ADM32 monitors the status of the patient and if fibrillation is detectedthen pulses from the biphasic pulse generator are delivered to thepatient automatically. In the advisory mode, the ADM32 monitors thepatient and generates audio and/or visual indication of the patient'sstatus, including an indication of a fibrillation episode, makes thedevice ready to deliver defibrillation pulses, however, defibrillationpulses are not applied unless they are delivered by the clinician. Inthe manual mode the operation of the ADM 32 is under the completecontrol of the clinician. In the pacer mode, the clinician selects thepacing protocol and delivers the pacing pulses to the patient. Theclinician enters the parameters required for all these operations viathe knob 56 and switches 58 in response to prompts shown in the display54. In the Figures, the same wires are shown for both sensing theintrinsic cardiac activity of the patient and delivering the highvoltage biphasic defibrillator pulses. Of course, separate wires,terminating in appropriate electrodes and/or pads may be used as well.In this manner, the ADM 32 can deliver defibrillation (or other kindsof), therapy to a patient using any of the protocols well known in theart. An external defibrillator describing some protocols that may beused is described in commonly owned co-pending application Ser. No.09/452,507 filed Dec. 1, 1999 entitled AUTOMATIC EXTERNALCARDIOVERTER/DEFIBRILLATOR WITH TACHYARRHYTHMIA DETECTOR USING AMODULATION (AMPLITUDE AND FREQUENCY) DOMAIN FUNCTION, now U.S. Pat. No.6,289,243 incorporated herein by reference. Of course other protocolsand modes of operation may be used as well.

Importantly, during its operation, ADM 32 continuously exchanges datawith the monitor 12 over the serial cable 38. For example, the ADM 32needs to generate a digital representation of the ECG for itsdetermination of the patient's status. This digital ECG is transmittedto the monitor for its display 18. Under the direction of themicroprocessor 66, the ADM 32 may send various other information to themonitor 12, including, for example, its current mode of operation(manual, advisory, automatic). The ADM 32 may also send data descriptiveof various stages of its operation, including data indicative of thestatus of the patient, the voltage on the capacitors of the biphasicpulse generator, time required to charge the capacitors to a nominalvoltage, time until the next pulse is applied, time expired since thelast pulse, number of pulses applied to the patient, readiness of theADM to apply a pulse, etc. The ADM 32 may also include a self-testingfeature. The results of this self test may also be sent to the monitor.The information sent to the monitor 10 may be shown immediately ondisplay 18, may be sent to the printer 28 for a hard copy and may alsobe stored in the memory of the monitor (not shown). In addition, thedata from the ADM 32 may be transmitted to other sites if the monitor isconnected to a network.

The monitor 10 may also send data to the ADM 32, includingacknowledgments of the data received. Typically monitor 12 may becapable of monitoring one or more physiological functions of the patientsuch as blood pressure, arterial pulse oximetry (SpO)₂, carbon dioxide(CO₂), respiration, and cardiac output. Some monitors may be capable ofgenerating a digital ECG signal. While it is expected that the ECGsignal detected by the ADM 32 through its electrodes may be morereliable, the external ECG signal from the monitor may be used as abackup in case the ECG signal cannot be detected locally, or as a meansof confirming the validity of the local ECG signal by the ADM. Moreover,the ADM 32 may be adapted to determine the condition of the patient andother information based on other physiological parameters of the patientas well. For example, the ADM 32 may use any of the physiologicalparameters derived by the monitor 12 to determine whether the patienthas a cardiac condition which needs therapy to be delivered by the ADM32. These other physiological parameters may be provided to the ADM 32by the monitor 12 as well.

In addition, the memory 68 may be insufficient for data loggingpurposes. Therefore the ADM 32 may send some data for storage in memory30 of monitor 12. The monitor 12 can then return this data to the ADM 32as requested.

As described above, the ADM 32 is adapted to perform a self-test and tomonitor the status of the patient. If the self-test indicates that theADM 32 may be malfunctioning, or if a patient condition is detectedwhich should be brought to the attention of the clinician, the ADM 32 isadapted to generate an alarm signal. This alarm signal may be used toactivate the audible and visual signals on the ADM 32 and/or the monitor12. In addition, these signals may be transmitted to a remote locationvia the communications network connected to interface 22. Thecommunications network may be a wired or wireless network. Therefore theterm ‘network’ is used herein very broadly to cover any analog ordigital communications network capable of transmitting information fromthe system 10 to another location, including local area networks, widearea networks, Internet connections, paging cellular telephones,telemetry, and satellite communications, just to name a few.

Some monitors presently available are designed so that they can beinterfaced with other apparatus, like the ADM 12 using a standardprotocol such as Spacelabs Universal Flexport Protocol. If no suchprotocol is available for a particular monitor, the ADM 32 can beprogrammed so that it can communicate with monitor 12 using the uniqueprotocol characteristic of the monitor 12.

In summary, an automatic defibrillator module is described which can beintegrated with a patient monitoring device such that the two can sharevarious functions. More specifically, the ADM 32 includes the componentsnecessary to analyze the condition of the patient and to generate, ifnecessary, therapeutic pulses. Data from the ADM 32, including a digitalECG and other signals indicative of the operation of the ADM 32 are sentto the monitor 12 for display, printing, and/or storage. Thus, the ADM32 may or may not have its own ECG display, a printer or data loggingmemory. It is expected that the overall combination of a monitor and ADMrequires less space, is cost-effective and very flexible since the sameADM can be used with many different patient monitors from differentmanufacturers.

In the embodiment described above, programming information for the ADM32 is entered using the controls on the face of the ADM while patientspecific information is displayed or otherwise provided on the monitor12. Of course other arrangements may be made as well. For example, theprogramming information may be entered from the monitor 12 and/or someof the patient specific information can be displayed by the ADM 32.Moreover, the ADM 32 may also incorporate a printer which may bededicated for information from the ADM 32 or may be shared by themonitor 12. Moreover, the ADM 32 may also be arranged to sense otherphysiological parameters besides ECG as well and to transmit the same tothe monitor 12.

Obviously, numerous modifications may be made to this invention withoutdeparting from its scope as defined in the appended claims.

1. A composite monitoring system comprising: a patient monitor includinga sensor arranged to sense a physiological characteristic of a patientand a signal processor coupled to said sensor and adapted to process thesignal from said sensor, said patient monitor having one of severaloperational sets of operational characteristics and generating an outputindicative of said physiological characteristics; and a defibrillatormodule adapted to be selectively coupled to said patient monitor, saiddefibrillator module including a pulse generator responsive to commandsto generate therapeutic pulses for the patient, and a data generatorarranged to generate indication signals indicative of an operation ofsaid defibrillator module, said defibrillator module being programmableto interface with several patient monitors having different sets ofoperational characteristics, said patient monitor being programmed tointerface said patient monitor based on said one set of operationalcharacteristics.
 2. The system of claim 1 wherein said output memberincludes a display generating visual images.
 3. The system of claim 1wherein said output is fed to a printer adapted to print a hard copy ofsaid output.
 4. The system of claim 1 wherein said sensor comprises acardiac sensor adapted to generate an external ECG and wherein saidpatient monitor is adapted to transmit said external ECG to saiddefibrillator module.
 5. The system of claim 1 wherein said sensor isadapted to sense at least one of the physiological parameters selectedfrom the group consisting of blood pressure, arterial pulse oximetry(SPO)₂, carbon dioxide (CO₂), respiration, and cardiac output.
 6. Thesystem of claim 1 wherein said defibrillator module includes adefibrillator display.
 7. The system of claim 6 wherein saiddefibrillator module includes a defibrillator display arranged toprovide information associated with the selection of said operationalparameters.
 8. The system of claim 1 wherein said defibrillator moduleincludes a selector arranged and constructed to allow an operator togenerate operational parameters for said defibrillator module, saidoperational parameters defining a mode of operation for saiddefibrillator module.
 9. The composite system of claim 1 wherein saiddefibrillator module is adapted to operate in one of an automatic,semiautomatic and manual modes.
 10. A composite monitor/defibrillatorunit comprising: a first external patient monitor having one of severaloperational characteristic sets; a physiological sensor to sense theintrinsic cardiac activity of a patient and to generate a sensor signalindicative of said intrinsic cardiac activity; a controller arranged toreceive said sensor signal and to generate corresponding commands; apulse generator arranged to generate therapeutic pulses for the patientin response to said commands; an output member associated with saidcontroller and adapted to generate output signals indicative of anoperation of the defibrillator, said output signals being selected fortransmittal to said external patient monitor for display; programmingmeans for programming said output member to generate said output signalsto match the operational characteristics of several patient monitorswith different operational characteristics, said programming means beingset to function with said first patient monitor; wherein saidphysiological sensor, controller, pulse generator and output member arecoupled electrically and mechanically to said external patient monitorto form an integral system.
 11. The module of claim 10 whereincontroller includes an arrhythmia detector arranged to receive saidsensor signal and to determine a cardiac condition of the patient thatrequires therapy.
 12. The module of claim 11 wherein said output memberis adapted to receive a physiological parameter detected by saidexternal patient monitor, and wherein said arrhythmia detector isadapted to receive said physiological parameter and to make adetermination for delivering therapy to the patient based on saidphysiological parameter.
 13. The module of claim 10 wherein said outputmember is coupled to said pulse generator and is adapted to generatesaid output signals to indicate generation of pulses by said pulsegenerator for said patient monitor.
 14. The module of claim 10 whereinsaid controller is arranged to define a plurality of modes of operationincluding a fully automatic, an advisory, a manual, and a pacing modes.15. The module of claim 10 further comprising an alarm circuit arrangedto generate an alarm signal indicative of one of a patient condition anda module condition.
 16. The module of claim 15 wherein said module isadapted to send send alarm signal to a remote location over acommunications network selected from a group consisting of hard-wirednetwork, a wireless network, a local area network, a wide area network,the Internet, a paging system, a cellular telephone system, a telemetrysystem and a satellite system.
 17. The module of claim 10 furthercomprising a display adapted to display said sensor signal.
 18. Acomposite defibrillator assembly comprising: a patient monitor adaptedto sense and display a physiological parameter, said patient monitorhaving a specific set of operational characteristics; and adefibrillator module arranged to be mechanically and electrically couplewith said patient monitor to form an integrated composite system andincluding: a controller arranged to receive a sensor signal indicativeof the intrinsic cardiac activity of a patient and to generatecorresponding commands, said controller being arranged to function withone of several patient monitors, said controller being set to match thespecific operational characteristics of said patient monitor; a pulsegenerator arranged to generate therapeutic pulses for the patient inresponse to said commands; an output member associated with saidcontroller and adapted to generate output signals indicative of anoperation of the defibrillator, said output signals being selected fortransmittal to said patient monitor for display; wherein said patientmonitor is operational without said defibrillator module.
 19. The moduleof claim 18 further comprising a sensor adapted to sense said sensorsignal.
 20. The module of claim 18 wherein said controller is adaptedfor receive said sensor signal from said external patient monitor. 21.The module of claim 18 further comprising a physiological parameterdetector that detects a physiological parameter, said controller beingadapted to transmit said physiological parameter to said externalpatient monitor for display and processing.